Precision casting



' a--'wax pattern, which ti i edistates Patent Q 2,930,089 C "PRECISIONCASTING Harold Garton Emblem,

Aston, Melbourne, Derby, England, assignors to Rollsgoytfil Limited,Derby, England, a company of Great No Drawing. Application November 26,1956 Serial No. 624,229

Claims priority, application Great Britain December 16, 1955 v, 12Claims. (Cl- 22-193) Such molds may be prepared from a slurry containinga refractory and a binding agent such as hydrolysed ethyl silicate. Thisslurry may be used to invest an expendable. pattern or alternatively theslurry may be poured round anon-expendable mold pattern, which isremoved by some mechanical means when the slurry has set. I

"The present invention seeks to provide an improved process which may befound particularly suitable for the preparation of molds or cores havingincreased strength.

According to the present invention a method of manufacturing a mold orcore for use in metal casting comprises forming a mold or core structurefrom a refractory material which is moistened with an aqueous solutionof sodium or potassium silicate and hardened by the action of carbondioxide, applying to the hardened refractory structure at least onethermosetting resin, andhardenin the resin by application of heat.

" The thermosetting resin may be dissolvedin ayolatile.

solvent in which case the heat may be applied by combustion of thevolatile solvent itself or alternatively the solvent may be allowed toevaporate at room temperature or be driven ofi? by the application ofheat from an exter- 'nal source. The hardening of the resin may incertain cases .be effected with the taneous with the heating.

One suitable resin is an unsaturated polyester resin with which may beincorporated other ethylenically unsaturated compounds such as styreneor methyl methacrylate;

The application'of the resin solution can be effected by dipping orspraying. It has been found satisfactory to make one application of theresin solution and thereafter to burn off the solvent; this process mayin certain cases be repeated. Phenol formaldehyde resins have been foundsatisfactory foruse in accordance with the present invention. ureaformaldehyde and melamine'types. vent for such resins is isopropylalcohol; such acetone, ethyl alcohol and methyl alcohol maybe used. Thepreferred resins are unsaturated polyester A suitable sol,-

resins for which a suitable solvent is benzene, and phenolformaldehyderesins which are or isopropyl alcohol.

The invention enables a mold or core to be produced havinghigh strengthbefore firing; this in the case of cores permits the incorporation ofthe core in a die in which an expendable wax, polystyrene or frozenmercury pattern is formed by'the introduction, of the pattern material.In the case of a mold, high strength prior to firing provides soluble inethyl alcohol Mickieover, Derby, and Jack may incorporate apreformed'core pattern applicationof pressure simulconveniently Othersuitable resins are of the' Other solvents This invention relates toimprovements in the preparer-1 tron of molds and cores for use in metalcasting processes.

. h 2 rigidity, minimising distortions which wo'uldpresent inaccuraciesin the cast part.

It has been found that'the addition of sugar to the aqueous solution ofsodium or potassium silicate accelerates the hardening action by'carbondioxide, and preferred methods according to the present invention usesuch an accelerator. A convenient amount of sugar is up to 5 percent byweight of the silicate solution. An amount of about 2 /2 percent ispreferred. The preferred sugar is cane sugar.

'The sodium silicate solution may be prepared by dis- If desired, thewater may contain a convenient amount being up to 30 dissolving solidsodium silicate in Water.

In order to give increased strength of'mold or core 7 when fired, astable silicasol may be incorporated in the sodium or potassium silicatesolution. One such silica sol is that known under the British registeredtrademark ddit n or er a iv lrit may bade ab s t pp y hydrolysedethylsilicate to the mold or corestructure beforeror af er th ha snin n .thee ia uc app tion 5 hyd o sed.thx si ia may conveniently be c d b d ppinnr.spray ngandis ef l for in s ng the strength of the mold orcore whenfired.

'cate in the refractory mix, to give silica and sodium or v burning oil?of the soiveni.

Preferably such ethyl silicate is hydrolysed under acid conditions.

In the methods according to the present invention the mold orcore willnormally be fired in the process of preparing the mold for casting, forexample in the range of 700 to 1000 a mold or core having excellentstrength properties can be obtained. A core may be fired in this mannerbefore it is incorporated in a die used to form an expendable pattern byintroduction of expendable pattern material such as wax into the die. i

In one preferred method of applying the invention for? precision castingprocesses. a refractory mold structure is formed around an expend themanufacture of molds for able pattern such as a wax pattern, ,by rammingthe 'refractory moistened with sodium vor potassium silicate 1 aroundthe pattern which is supported within an outer casing. After hardening"by forcing CO gas into the l damped refractory, the hardened refractorystructure is removedfrom the casing and has the resin solution appliedthereto to absorb the latter with subsequent burning Advantageously, thesilicate solutions off, of the solvent. used may contain sugarl Likewisein the formation of cores, thedamped re fractory may be compacted inasplit die into which carbon dioxide is passed to harden the refractory;thereafter the refractory core structurei is' removed from the die, andpplied thereto with subsequent "Alternatively, the solvent may has theresin solution: a

be allowed to evaporateg nd the resin cured'by the application of heat,with tion ofpressure. m I

' Carbon dioxide reacts withsodium and potassium Sflie potassiumcarbonate, thereby binding the refractory struc ture which is of aporous nature capable of absorbingthe resin solution. The hardening ofthe resin increases the -low-temperature;strength of the resultant moldor] core prior to firing.

" Patented Mar. 29,1960

which should be powdered to increase its rate of I observed that moresugar is necessary if the sodiumsilicate solution isprepared by C. Inthis manner it'has been found-thator without the simultaneous applica Asuitable commercially available aqueous sodium silicate-solution-has thefollowing properties:

Na O percent by weight 15.2 SiO Y 7 7 do- 30.4 Molecular ratio, SiO'/Na- O' 112105 Density at 20 C. 1156' Viscosity at 201C. 'centipoises..900

A cornmerciallyyavailable aqueouspotassium silicate solution hasaKQzsiOratioof 112.0 by-weight, withla' specific gravity ofaaboutzlJ.

Ithas been found] thatusingsuch commercially avail? able. silicate.solutionsg. refractories: cant be, satisfactorilydamped for use inaccordance with the inventionby add ing about,3.p.ercent1 or more up toIOpercent byweight of the solution in theiweiglit of: the. refractory;mix.

Various. refractories. may be: used, one preferred refractorybeingzircon. Zirconis. ofga highly refractory nature, has relatively.low-expansionon heating,,and' has been found to give-strong molds.

Other refractories which. are preferred. are; silicaalumina,sillimanite, andcalcinedfireclay grog having an alumina content ofatleast/1 A sieve analysis of one particular.- mixture of zircon sand andzircon flour used. in methods according tothe present invention isasfollows. (the sieve numbers quoted being in accordance with. BritishStandard. Specification .410 of Sieve No.: Percent'retained 44 Y 011 600.4 100 1919 150 61.5 200 I a 7.2 300 0.6- Pass 300 10.1

In making up an investment material, zircon refractory according to theaboveanalysis comprises approximately. 90-97 percent (by weight) of themix,.whilst.sodium or. potassium silicate solution with sugarsuchasthosementioned represents the remainder.

In another method of making up an investment material, 100 parts byweight of'zircon refractory according to the above analysis, aremixedlwithtwo'parts by weight of finely powdered sodium metasilicatepentahydrate, and two parts by weight of an aqueous sugar solutioncontaining 25 percent by weightofcane. sugar. Mixingshould continueuntil the refractory material is thoroughly damped.

In order to give increased strength to the mold or core after firing, astable silica sol may be added to the silicate solution. Thus'in onepreferred process according to the invention sodium silicate solution ismade up as follows:

Stage I.-200 gms. of" stable silica sol sold under the registeredtrademark Syton as Syton 2X are added to 20 gms. of sugar.

Stage 2.To 300 mlof the commercially available sodium silicate solutionspecified aboveare added 100 ml. of Syton 2X and sugar solutionpreparedin stage 1 above. It is cssential-tostir vigorously during thisaddition.

This sodium silicate. solution is thenadded .todamp a refractoryaccording to the above sieve analysis, 3. percent to percentofthesolutionby weight beingused. in 97 percent to 90 percent by: weightof refractory.

In another preferred process according to the invention. potassiumsilicate solution is made up as follows:

Stage 1.-20 gmshoftsugar...aredissolvedin 200ml. of a stable silica. solsold under. the Britishmregisteredc trademark Syton as Syton 2X..

Stage 2.To. 300. mL. of. aqueous. potassiurnsilicate. solution specifiedabove are addedlOO ml. of .the.Syton 2X and sugar solution. prepared instage 1. above. It is essential to stir vigorously during thisaddition.v

Syton 2X is a silica aquasol having the following properties:

Silica content I percent pH Average particle diameter. 250 A.

Where the inventionis used to formamold around an expendable pattern,the latter may be given an initial coatingot" a fine refractory-boundmaterial, eg by spraying or:

dipping,. one: of the kn'own. coating compositions being used;Suchcoating may be dusted with a coarse refractory before investment,and may be strengthened by dippinginuacid hydrolysed ethylsilicatesolution, as describedin our 'co-pending British application No.3,136/54 and the corresponding US. application 483,164 filed I anuary20, 1955', now abandoned.

An example of a resin solution is as follows:

Benzene ml 5 Styrene (monomer) ml 11 Unsaturated polyester resin ml 45Catalyst gms 3.25 Accelerator ml 2 In the above composition benzene isthe volatile solvent. An alternative composition, free of'solvent, is:

Styrene (monomer); ml'. 40 Unsaturated: polyester. resin ml 60 Catalystgms 2 Another unsaturated'polyester resin composition, free of-solvent,is:

Unsaturated polyester resin 300 Methyl methacrylate 50.

Styrene 30 Before use, add 12 ml. ofLbutyl .perbenzoate to 350 ml. of.the. above composition- Hardening iscompleted by heat ingfor 15-24 hoursat .70? C.

Another example of'a resin solution is:

Percent by weight Spirit soluble-.phenol-formaldehyde resin 1O Ethylalcohol, or isopropyl alcohol Hardening of the resin may be completed byburning off the solvent. This solution is particularly. suitable for.use where more than one application is desired.

It will be understood that in the case of a mold formed around a waxpattern the burning off of the solvent if such a solvent is used andburnt off will normally result in the removal of'the wax, final tracesof. the wax being removed by firing -for example in the range of 700 to1000C.

Preformed refractory, cores'made according to the present invention canbe incorporated in the expendable pattern prior to firing.which istheninvested accordingto theprocess of this invention or in an alternativeinvestment material'such as the known hydrolysed ethyl silicate boundrefractory. Alternatively the pattern with the core incorporated thereinmay be invested by a dipping process. as for example described in UnitedStates application Serial No. 376,243, filedAugust 24, 1953;. now US.Patent. No..2,80'6,'269. granted to. Adam Dunlop, September 17, 1957.

By the. expression a stable silica sol used inthis specificationtherb:is meant. a stable. substantially electrolytefree colloidal dispersionof silica in water, sometimes referred to as a silica aquasol."

We claim: I

1. A method of manufacturing, for casting metals, 8. high strengthbefore firing mold structure from a refractory material which includesmoistening finely divided refractory material with from 3 to percent ofits weight of an aqueous solutionof a silicate of a metal selected fromthe group consisting 'of. potassium and sodium, forming a mold structuretherefrom, hardening the same throughout by the action of carbondioxide, applying to the surfaces of the hardened refractory structure anon-aqueous solution of at least one thermo-set ting resin and hardeningthe resin by the application of heat to the structure, and then firingthe mold structure at a temperature in the range of 700 to 1000 C.

2. The method claimed in claim 1 in which the thermosetting resin isdissolved in a volatile solvent.

3. The method claimed in claim 1 in which the silicate solution containssugar as a hardening accelerator up to an amount equalling 5 percentby-we'ight of the silicate solution.

4. The method claimed in claim 1 in which up to 30 percent by volume ofa stable silica sol is incorporated in the silicate solution.

5. The method claimed inclaim 1 in which the resin is applied as asolution inbenzene of styrene resin (mon- 12. A method of manufacturinga mold for casting v metals comprising forming an expendable pattern,coat ing the expendable pattern with an initial refractory coating,investing the coated pattern with refractory rnaterial which ismoistened with an aqueous solution of a silicate of a metal selectedfrom the group consisting of omer), a larger quantity of unsaturatedpolyester resin and a catalyst. I

'6. The method claimed in claim 1 in which the resin solution comprisesa phenol-formaldehyde resin dissolved in a solvent selected from thegroup comprising methyl alcohol, ethyl alcohol, and isopropyl alcohol.

7. A mold structure for casting metals formed 'by the method claimed inclaim 1.

8. The method claimed in claim 2 in which the solvent is flammable andthe heat to cure the resin is supplied by burning off the solvent.

9. The method claimed in claim 5 in which the catalyst is butylperbenzoate.

10. The method claimed in claim 5 in which the resin compositionincludes methyl methacrylate.

11. The method claimed in claim 5 in which the catapotassium and sodium,which solution forms only a small percentage of the m'urture, forming arefractory mold structure therefrom, hardening the same byfthe action ofcarbon dioxide, applying to the hardened refractory structure anon-aqueous solution of at least one thermosettingresin, and hardeningthe resin by application of heat.

References Cited in the file of this patent UNITED STATES PATENTS2,313,674 Salzberg et'al. Mar. 9, 1943 2,380,945 Collins Aug- 7, 19452,391,855 Bean .Dec. 25, 1945 2,521,839 Feagin Sept. 12, 1950 FOREIGNPATENTS 8,180 Great Britain Sept. 19, 1911 of 1911 11,568 Great BritainAug. 23, 1884 of 1884 p 15,619 Great Britain Apr. 15, 1899 of. 1898688,652 Great Britain Mar. 11, 1953 710,099 Great Britain June 9, 1954716,394 Great Britain Oct. 6, 1954 741,381 Great Britain Nov. 30, 1955745,402 Great Britain Feb.' 22, 1956 OTHER REFERENCES Hardening Sandwith CO Pursall et al., Foundry,

